The present invention relates to a surface-pressure generating device, for use particularly in an injection-molding machine, having a stationary platen, and a movable platen which can be moved linearly in relation to the stationary platen, guided by tie bars. Material to be compressed, or molds to be clamped are arranged between said moving platen and said stationary platen.
Surface-pressure generation, in which a movable platen rests on a platen which can be arrested in an operating position, is generally disclosed in DE 43 36 572 C2. Here, the stationary platen and movable platen for an injection-molding machine are jointly moved relatively rapidly by a first traversing mechanism, then the stationary platen is arrested in the operating position. The injection-molding operation is started. To support the forces emanating from the flow front of the polymer, the movable platen is moved by a second traversing mechanism. While the first traversing mechanism is intended to bring about rapid movement over a relatively long path without strong force, a relatively high force is initiated by the second traversing mechanism over a short path. The first traversing mechanism is usually either a hydraulic drive or an electromotive drive, in which the rotary motion of the electric motor is converted into a linear motion by a gear mechanism. Although a hydraulic drive can initiate a linear motion relatively easily, it requires the use of special hydraulic fluids, which are not always desirable. Also, the use of a conventional electric motor means that the original rotational motion of the rotor first has to be converted into a linear motion.
The object of the present invention is to design a surface-pressure generating device in such a way that a rapid traversing mechanism is designed so as to be technically simple. This object is achieved in the present invention by arranging the primary part of a linear motor for the linear traversing on at least one of the tie bars; and with the secondary part of the motor being realized by the other tie bar. As a result, it is possible to realize a drive just by adding a primary part of a linear motor into the construction. The mechanisms are simply incorporated into the drive. The German text of the originally filed application is incorporated herein by reference.
It has been found to be advantageous if the linear motor is designed as an asynchronous motor, since there is no need for a special design of the tie bars, as would be necessary for synchronous operation. Moreover, the fact that the primary part of the linear motor is cylindrically engaged around the respective tie bar means that a high motor output can be achieved with a small volume.